Conventionally, a technique for performing communication with, for example, a telephone, a facsimile, and internet, via an artificial satellite has been known. Communication via an artificial satellite (satellite communication) is used in an area (sea, a remote island, etc.) where neither of wired communication facilities nor wireless communication facilities are equipped. JP2006-527926A discloses a technique which is used when utilizing satellite communication in aircrafts, etc.
In JP2006-527926A, the technique enabling telephone conversation and communication in aircrafts via mobile phones is disclosed. Specifically, an aircraft has an antenna for satellite communication. The satellite communication connects a network for mobile phones inside the aircraft with a network for a base station on the ground. Thus, telephone conversation and communication are also available in the aircraft by using mobile phones.
Meanwhile, for satellite communication, a measured rate system in which the fee is determined based on a communication volume, airtime or the like is adopted. In this case, if the satellite communication is always available, the communication fee becomes high. Therefore, in JP2006-527926A, a configuration using an emulator is disclosed.
Even when the network for mobile phones is not connected to the network for the base station, the emulator can operate as if they are connected to each other. Thus, when neither of the telephone conversation nor the communication is performed using the mobile phones, or when the information that neither of the telephone conversation nor the communication is performed is not required to be transferred to the ground, the communication fee can be reduced by disabling the satellite communication.
Meanwhile, a protocol referred to as an ICMP (Internet Control Message Protocol) has been known conventionally. The ICMP is a protocol for notifying to a source host, information and the like regarding an error caused before a packet reached a destination, or the communication regarding the packet. Note that, hereinafter, a server which supports (respondable to) packets using the ICMP is referred to as an ICMP server.
As communication using the ICMP, a ping is known, for example. The ping utilizes an echo request and an echo notification of the ICMP. The ping transmits an ICMP packet to other terminal and ICMP server and the like with which network communication is desired to be checked, and checks whether the packet arrives appropriately based on whether a response to the ICMP packet is received. By utilizing the ping, for example, it can be monitored whether the line to the ICMP server is alive.
Here, in failover systems (a collective term of systems where one of the systems cannot be used, another one of the systems is used), in order to grasp a line status in a simple method, normally, the life-and-death monitoring of the main line is performed using the ICMP packet. However, in this case, if the measured rate system is adopted to the main line, a communication fee will be charged.
Note that, as long as the method of checking either one of the availability of the communication and the communication environment by actually performing satellite communication is adopted, methods other than the ping also have this disadvantage.